Blog Archives

Highway Superelevation

Superelevation is the banking of roads through turns so that the lateral forces on the vehicle balance out with the centrifugal force during the turn. Proper superelevation will allow a vehicle to safely turn at high speeds and will make riders comfortable.

From the AASHTO Green Book:

Urban areas the maximum superelevation is 4% to 6%.

Ice and snow areas the maximum is 6% to 8%.

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Vertical Curves

Vertical Curves are nice! I think they are easier to solve than Horizontal Curves because they are essentially parabola equations (which you should be very used to). This is the formula for vertical curves

$$ y(x) = y_{PVC} + G_1x + \frac{1}{2}Rx^2 $$

\(y(x)\) is the elevation y at x horizontal distance into the curve from the start position

\(y_{PVC}\) is the starting elevation at x = 0.

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Horizontal Curves Definitions and Formulas

Horizontal Curve Formulas

$$L = 100\frac{I^{\circ}}{D^{\circ}}$$

$$L = RI_{\text{radians}}$$

$$L = \frac{RI 2 \pi}{360^{\circ}}$$

$$ R = \frac{5729.578}{D}$$

$$ T = R\tan\frac{I}{2}$$

$$ LC = 2R\sin\frac{I}{2}$$

$$ E = T\tan\frac{I}{4}$$

$$ M = E\cos\frac{I}{2}$$

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